Process of making fluorinated acyl fluroides



United States Patent PROCESS OF MAKING ELUORINATED. tACYL FLUORIDES.

Thomas]: Brice; St. Paul; and Wayne A. Severson, Little Canada; Minn}, assignors to Minnesota Mining & Manufacturing Company, sr. .1!aur,-.nnnn., a corpora? tion of Delaware:

No Drawing. Applicationiseptember 1, 1954,

Serial No. 453,679

S CIaimSa (Cl; 260-408) This inventionrelates to our discoveryof a new and useful process ofm-aking certain fluorinated acyl fluoride compounds.

More particularly,- in the.product compounds of our hereinclaimed process, the carbonyl fluoride group (-COF) is Bonded to a perfluoroallc'yl" chain, arm a c'hloroperflu-oroa'lkyl' chain; containing 3" to 1'1- carbon atoms,.there' being 4'10 12 carbon atoms-in the compl'ete molecule. p

The term perfluoroalkyl" signifies a saturated flnorm carbon group consisting solely of. fluorine and" carbon; having the formula ChF2n+1 -,.WliiCh may be regarded" as. a fully fluorinated alkyl group (all hydrogen atoms having been replaced by fluorine. atoms); The" term ch'loroperfluoroa'lkyl signifiesa' saturated group:consist= ing solely of'chlorine', fluorine; and: car'h'on,i in* which there.

are fewer chlorine atoms'than fluorine" atoms and each carbon atom is bonded-to 'at'least': one fluorine atom, constituting a stable and inert structure having. modified fluorocarbon characteristics. These chloroperflnoroalkyl chains, as 'well' as the fully. fiuorinated' (perfluoroalk'yllf chains, are suflieiently inert andEstabl so that a. good yie1d can beaobtaiued' by our process firom'a correspond ing'. starting. compound that contains the same chain.

The starting compounds us'ed'inriur. process correspond to the product compounds except that they containa terminal diflnoromethylgroup (j-CF'zH')', which is convert'ed by the process to a carbonyl fluoride group -COF). The acyl fluoride product compounds canbej readily. converted to desirahle derivatives, such as the correspondingcarboxylic. acids andsal't's'.

Thus our starting compounds can be. generically d'ehired as Being. compounds of the class consisting; of per-f fiuoroalkyldifiuoromethyl and chl'oroperfluoroalkyldifluoei rome'thyl compounds, containingA' to 12 carbon atoms in. the molecule.

We have foundlthatthe'se starting'compounds. can be converted to the correspondingacyl' fluoride product com pounds in good yields by asiniple procedure involvingthd thermal'reaction in vapor phaseof the tluor'inated starting compound with a mixture of nitrogen dioxide. (or nitric.

sentdbyth'e following equation:

NO; or N O ROOF The present availahility of starting compounds makes the process: ofparticularvalue? (A) For converting perfluoroalkyldifluoronrethyl startin'g compound's to the corresponding perfiuoroalkanoyl Thewstarting compounds are obtained. asIby-productszi-n;

they operation; of-. the Simons electrochemical fluorination process (cf., U.Sl PatentsNos. 2,519,983 and.2,5'67,011.). (13), For converting omega-monochloroperfluoroalkyb difiuoromethyl starting compounds to the corresponding omega-monochloroperfluoroalkanolyl..fluorides:

These starting compounds are describedin U. S. Patent No. 2,551,573 and in the paper of Ji- D. Park etalt published in Iudustrial.andEngineering' Chemistry, voli 39, p: 354*(March11947i);

In the two above. equations n (the number of'carhon atoms in the'inertifluorinated. alkyl chain) has aninteger value of 3to 11; the product compounds having. a. total of4to 12 carbon atoms in the molecule;

These two: equations" can he represented generically by the equation where X stands for F or Cl.

'Flie perfluoroalltanoyl fiuoride products of the process, and corresponding carbonyl derivatives such as the acids and salts, are described initheaDiesslin, Kauck and Simons Patent No. 2,567,011 (September 4, 1951) and irra paper hyyKauck and'Diesslin puhlished'iin lndustria'lfandEngineering- Chemistry; vol. 43",, pp. 2332-2334" (October 1951); The presentprocess: provides a new' route to their preparation:

The omega-monochloroperfluoroalkanoyl fluoride prodnets of the process; containing 4 try-12" carbon atoms in the molecule, and corresponding carbonyl derivatives, suchassthe: acids, l(F2:)nCQOH, and: salts;

Cl(CE)"nCOOM are. believed. toibe. novel; compounds... So far as: we are aware; the present. process is the only practical route totheir preparationrthusz far; discovered; These novel. compounds have; valuerasrsurface: active agentsanrr as-zstarte ing compounds for makingsurfaee: active agents.

A feature. of ourprocess; is its simplicity; Good results: can be: obtained; by merely passing. a:. gaseous mix.- ture ofrthe fluorinatedstarting-,compoundNQz (orNQ); and Clz-(or Brziathrough an empty tube-which is maim tained. at a: temperature: of 11161011161 of; 500. to 65.0. CL Tubes of nickel, nickel alloys, stainless steel, mildrsteel, and. platinum. can be: employed. A reaction contact. time oflessthan 30 seconds. has; been found. suiticientto pro.- duce' a substantially?- complete conversion and a useful yield: The. minimum: amount. of. reactants; theoreticallyneeded is. onemoleof N02 or'NO'and one-half mole-of C1: or Brzper moleofthe;fluorinated-starting compound. However: it. ispreterredihat ratios. somewhat in excessnofi this be. used. A chargingmixture of N02 and-N0 can. be usedin place. of. either. alone. It. may. be notedihat. whentNOa is used,'. dissociation. resultsin. a mixture of N02 and. NO in the reactionzone. The gas mixturefeed stock. can he diluted Withau inert. gasifj desired. Reactants. can be supplicdbyusing compounds that decome pose: in the reaction zone, or in advance thereof, to. form them in situ'. The nitrosyl and nitryl halides; NOCL. NOB'r; NOCl and NOzBr, should be. useful. since they decompose to, give 'Clzor. Brz and NO or. N02, for in-. stance. The prefrredreactants are nitrogen dioxide and. chlorine: Good results have been obtained with. mole: ratios of about 1:332 for the fiuorinated starting com.- pound, nitrogen dioxide, and chlorine, respectively, Although thereaetion can'be satisfactorily performed-in an empty tube and without theme of a catalyst,1the* use of packed tubes=and of catalysts is not precludedi The comhination ofth'e ahove mentioned NOa-orgNO and 'Cla or'B'ra reactants has apeculiar utility "in our' proc; ess. TheNOz: or NO is ineffective in the ab'senceof chlorine or bromine, and iodine does not work. If chlorine or bromine were used alone, the product would be a chlorinated or brominated compound resulting from replacement of the hydrogen atom with a chlorine or bromine atom (see U. S. Patent No. 2,658,928). Nor is the result obtained merely on account of the N02 (or NO) being an oxygen-containing oxidizing agent, since air, oxygen, nitrous oxide, sulfur dioxide andsulfur trioxide are not useful substitutes. So far as we are aware, our process is the only one thus far discovered by which our starting compounds can be converted to the corresponding acyl fluorides in good yields.

The reaction product mixture, after leaving the reaction tube, can be condensed and the fiuorinated acyl fluoride product recovered by fractional distillation. However, it is not necessary to recover this product as such, especially as it will ordinarily be employed in making a derivative. It can be usefully recovered by treating a reaction product mixture so as to convert it to a derivative that is recovered, as by hydrolyzing with a base to form the corresponding carboxylate salt, or by hydrolyzing with water to form the corresponding carboxylic acid, which is recovered.

The following experiments are illustrative of our process.

Example 1 In this experiment C'IFHH was converted by our process to CsFrsCOF, which was recovered as the acid, CeFrsCOOH, employing N02 and C12 as reactants. The thermal reaction can be written as follows:

The reactor was an empty nickel pipe 1 inch in diameter and 21 inches long, mounted in an inclined position in a 13 inch electric furnace. The temperature was measured with a thermocouple embedded midway in the wall of the pipe. The NO: and Cl: were metered at controlled rates through flowmeters, and the C'IF15H in liquid form was continuously mixed into the gas stream from a calibrated burette and vaporized to provide the gaseous mixture charging stock, which was fed in through a tube connected to the upper end of the reactor pipe. The exit (lower end) of the reactor pipe was connected to a trap cooled with ice, and the volatile products passing from the latter were condensed in a liquid air trap. The experiment was conducted at atmospheric pressure.

The reactor tube was maintained at a center wall temperature of approximately 600 C. The charging stock was passed through it during a period of 15 minutes and consisted of 24.7 grams of CrFrsH, 6.6 grams of N02, and 5.2 grams of C12. The liquid product collected in the ice-cooled trap weighed 17.8 grams, and contained the CsFraCOF reaction product (perfluoroheptanoyl fluoride), and a minor proportion of CsFuCOF by-product, together with small amounts of other materials. This fraction was hydrolyzed by being poured into 100 ml. of cold water contained in a separatory funnel, and the mixture was acidified with 25 grams of concentrated sulfuric,

acid to cause separation ofa lower phase containing the fiuorinated acid. To ensure that no fiuorinated acid remained in the upper water phase, addition was made of 125 ml. of c-CsFrzO, a water-insoluble inert cyclic fluorocarbon ether (cf., U. S. Patent No. 2,644,823) in which fluorocarbon acids are soluble, which settled to the bottom carrying with it any acid extracted from the water. The lower layer of fluorocarbon ether and acids was removed and the fluorocarbon ether was evaporated off by gentle heating under vacuum.

The crude acid was subjected to fractional distillation, resulting in a fraction having a boiling range of 170-175 (at 740 mm.), weighing 11.1 grams, identified as relatively pure pertluoroheptanoic acid, CsFuCOOH.

4 Example This experiment illustrates the use of bromine.

Using the same apparatus, with the center wall temperature maintained at approximately 600 C., a charging stock containing 10.1 grams of C7F15H, 3.7 grams of N02 and 7.0 grams of Brz, was passed through the tube during a period of 8 minutes. The liquid collected in the ice-cooled trap weighed 8.3 grams; The excess NO: and Bra contained in the liquid was removed by adding mercury and the precipitate was separated by filtration. The liquid was subjected to hydrolysis and the product was found to consist mainly of CsFnCOOH.

Example 3 This example illustrates the conversion of chloroperfluoroalkyldifluoromethyl compounds. Specifically, it illustrates the conversion of Cl(CFz)aH to Cl(CFz)5COF, and the hydrolysis of the latter to CI(CF2)5COOH. The thermal reaction can be written as follows:

NO: 01(C F:)rC F 11 ET 01(0 FmCOF Using the same apparatus, with the center wall temperature maintained at approximately 550 C., a charging stock containing 25.2 grams of Cl(CF2)sH, 10.4 grams of N02 and 7.9 grams of C12, was passed through the tube during a period of 23 minutes. The liquid collected in the ice-cooled trap weighed 21.0 grams, and contained the desired CI(CF2)5COF, omega-chloroperfluorohexanoyl fluoride, in a yield of 72%. Fractional distillation resulted in recovery of this compound in relatively pure form (B. P. of 81 C. at 740 mm.) together with a fraction identified as the corresponding acid (B. P. of ISO-183 C. at 740 mm.), namely,

Cl(CF2) sCOOH,

omega-chloroperfiuorohexanoic acid, which had been formed as the result of moisture from the atmosphere, or water present as a by-product of the hot tube process, hydrolyzing some of the acyl fluoride.

This acid had a refractive index at 25 C. of 1.3280, and a neutral equivalent value of 326 (calc. 330). Analysis showed 11.2% C1 (calc. 10.8%). The terminal chlorine atom elevates the boiling point by about 25 C., since the boiling point of the corresponding fully fluorinated acid, F(CF2)5COOH, is 156 C. The surface activity of this omega-chloro acid is indicated by the fact that it reduces the surface tension of water at 25 C. from 72 dynes/cm. to a value of 40 dynes/cm. at a concentration of 1% by weight. It is a strong stable acid and carbonyl derivatives, such as acid anhydrides, acid chlorides, metal and ammonium salts, esters and amides, can be prepared by methods used in making the derivatives of the corresponding fully fiuorinated acids (see U. S. Patent No. 2,567,011). The higher members of the series have even stronger surface active properties owing to the greater length of the chloroperfluoroalkyl chain which is both hydrophobic and oleophobic. These acids can be employed instead of fully fiuorinated acids in making chromium coordination complexes, as by employing the procedure described in U. S. Patent No. 2,662,835 (December 15, 1953), to obtain complexes useful for treating papers, textile products, glass and metals, to provide surface coatings that are both waterrepellent and oil-repellent.

Example 4 This example illustrates the preparation of a higher member of the omega-chloroperfluoroalkanoyl fluoride series and the corresponding acid.

Using the same apparatus, with the center wall maintained at a temperature of approximately 550 C., a run was made employing a mixture of Cl(CF2)sH, NO: and C12 in a mole ratio of 1.0:6.7:3.4. The liquid condensate was found to contain the desired CI(CF2)1COF,

omega-chloroperfluorooctanoyl fluoride, in a yield of about 40%. It was hydrolyzed to form the corresponding omega-chloroperfiuorooctanoic acid,

The latter is only slightly water-soluble and is a solid material having a melting point of about 50 C. The neutral equivalent value was found to be 428 (calc. 430.5). Analysis showed 8.4% Cl (calc. 8.2%). This S-carbon acid has a markedly higher surface activity than does the 6-carbon acid of the preceding example.

We claim:

1. A process of making fluorinated acyl fluoride compounds which comprises thermally reacting in vapor phase a starting compound of the class consisting of perfluoroalkyldifluoromethyl and chloroperfluoroalkyldifiuoromethyl compounds containing 4 to 12 carbon atoms in the molecule, with a mixture of a reactant of the class consisting of nitrogen dioxide and nitric oxide and a reactant of the class consisting of chlorine and bromine.

2. A process of making a perfiuoroalkanoyl fluoride compound having the formula:

F (CFz) nCOF from a corresponding perfluoroalkyldifluoromethyl starting compound having the formula:

F (CFa) nCFaI-I Cl( CF 2) nCOF from a corresponding omega-chloroperfluoroalkyldifluoromethyl starting compound having the formula:

Cl (CFa) nCFaH where n has an integer value of 3 to 11, which comprises passing a gaseous mixture of said starting compound with at least one mole of N02 and one-half mole of C12 per mole of said starting compound, through a heated reactor tube maintained at a temperature of about 500 to 650 C.

References Cited in the file of this patent UNITED STATES PATENTS Hart et al. June 14, 1949 OTHER REFERENCES Unit Processes in Org. Synthesis (Groggins), McGraw- Hill Book Co., Inc., N. Y. (1952), pp. 421-426. 

1. A PROCESS OF MAKING FLUORINATED ACYL FLORIDE COMPOUNDS WHICH COMPRISES THERMALLY REEACTING IN VAPOR PHASES A STARTING COMPOUND OF THE CLASS CONSISTING OF PERFLUOROALKYLDIFLUOROMETHYL AND CHLOROPERFLUOROALKYLDIFLUOROMETHYL COMPOUNDS CONTAINING 4 TO 12 CARBON ATOMS IN THE MOLECULE, WITH A MIXTURE OF A REACTANT OF THE CLASS CONSISTING OF NITROGEN DIOXIDE AND NITRIC OXIDE AND A REACTANT OF THE CLASS CONSISTING OF CHLORINE AND BROMINE. 